I'm with those who would press the "dislike" button on this, if there was one.
I fly with easyJet and Ryanair all the time, and one of the big advantages is to turn up reasonably early (and that's the key thing... reasonably)... wander down to the gate as soon as it's announced, get as close to the front of the non-priority / speed boarding queue as possible, nip in the back door, and get the overwing exit row seats. If families and groups want to sit together, then there's nothing stopping them getting down to the gate early and doing likewise. I mean, seriously, you have to be in the last 20% or so of people on the plane to not be sitting next to at least one other person with you.
All this is doing is pandering to the idiots who faff around in the duty free shop / restaurant / cafe / bar until the last minute and then saunter onto the plane, which should have left 5 minutes ago. While p*ssing off the rest of us who played by the rules and got there early. Ryanair will be getting much more of my business should this silly plan go ahead.